The present invention relates generally to a doctor blade extractor for doctor blades used in papermaking machines.
Doctor blades are well known and are used where revolving rolls are employed to move or form paper. These blades are made of metal, plastic, and graphite fiber. The doctor blade is placed in contact with the revolving roll to keep the roll clean and/or shed the sheet. The blade must be flat, straight and parallel, and its composition must be compatible with the roll to be doctored. Because they are in contact with the roll, the edges of these blades get sharpened to a near razor sharpness.
The blade holder exerts a uniform load pressure on the blade. It holds the blade firmly against the roll, accommodates roll irregularities, and within limits, compensates for thermal expansion. Doctor blade holder designs normally comprise a body member having a slot adapted to receive a doctor blade with the doctoring edge of the blade projecting from the open end of the slot. The blade is normally mounted in the holder with a series of fasteners.
A common problem with known blade holders, however, is that the restrict the extraction of the blades from the holder. In some cases, the holder must be removed from the paper machine to remove the blade. This requires extensive manpower and machine downtime. After removing the blade, the assembly must be re-installed in the paper machine, consuming more manpower and time. Further, in many cases, the blades are installed in locations that require a long reach across a paper machine frame or other equipment, and they are situated in such a way as to make the attachment of most mechanical devices used for extraction difficult.
Doctor blade holders generally are not provided with a tension relieving mechanism, and the blades are held by a considerable amount of friction making the removal difficult and dangerous. A wide machine further compounds this problem by adding the added length of the holder and therefore a corresponding amount of added friction to the removal of the blades. In addition, the build-up of scale and debris, particularly in holders where the blades are not removed frequently, further adds to the friction. Chemicals used in paper making also compounds the problem by corroding the holder and blade.
Another problem is that sharp doctor blades are known to cause injury. Blades can be located in areas where a reach across the frame of a machine is required to access the edges of the doctor blades. This length of reach can exceed the length of a normal person""s arm. Reaching an arm into locations that are dimly lit and small in their opening can result in personnel injuring themselves on sharp metal edges of the machine.
Current methods of extraction employ tools that a generic in nature, such as the tool sold under the trade name VICF GRIP. In general, these tools only grip and hold a blade by way of downward friction force. However, such devices can slip when sufficient tension is applied to the extraction of the blades, simultaneously being ineffective and posing a serious safety risk. Another current method of extraction uses a hook similar to a cargo hook that fits into a xe2x85x9xe2x80x3 hole drilled in the ends of doctor blades. If the hook can be inserted in this hole, then the hook can effectively be employed. However, many blades are in locations that cannot be accessed by the hook. This requires that the blade be forced out about four to five inches from the back side of the machine by personnel before the hook can engage the drilled hole. This procedure uses added personnel and takes added time.
It is, therefore, an object of the present invention to overcome these deficiencies of the prior art and to provide an improved doctor blade extractor. Another object of the invention is to provide a safer, more effective, and reliable mechanism for removing a doctor blade from its associated holder. These and other objects of the present invention will become apparent from a review of the description provided below.
The doctor blade extractor of the present invention provides an effective and reliable mechanism for removing a doctor blade from an associated holder. In particular, an extractor consistent with the invention may include a head portion including at least one gripping member, and a linkage shaft. The linkage shaft is coupled to the at least one gripping member and is movable relative to the head portion between a closed position wherein the at least one gripping member is positioned to engage a doctor blade, and an open position wherein the at least one gripping member is positioned to release the doctor blade. A locking member may be provided for releasably locking the linkage shaft in the closed position.
The linkage shaft may be slidably disposed in a hollow shaft, and a trigger extending from the linkage shaft through a slot in the hollow shaft may be provided for moving the linkage shaft between the open and closed positions. The linkage shaft may be biased into the closed position by a spring coupled thereto. The locking member may include a locking ring having threads thereon for meshingly engaging corresponding threads on an interior of the hollow shaft, and the locking ring may be rotatable into the hollow shaft for engaging the linkage shaft in the closed position.
In one exemplary embodiment, the at least one gripping member may include a pivoting cam shoe coupled to the linkage shaft through a pin. The head portion may further include a stationary platform shoe, and the cam shoe may be adapted for forcing the doctor blade against the platform shoe when the linkage arm is in the closed position. In another exemplary embodiment, the head portion may comprise a yoke coupled to the linkage shaft and first and second pivot arms coupled to the yoke. The pivot arms may be attached to first and second ones of the gripping members. The first and second gripping members may be fixed about first and second associated pins that ride in associated slots in the head portion.